The implantology which comprises the insertion of artificial materials such as artificial organs, artificial blood vessels, artificial joints, artificial bones and artificial tooth roots into living bodies so as to recover lost parts of living bodies or their functions has received much attention in recent years. It is said that a trial of implantation goes back to ancient times. Particularly in these ten-odd years, a huge number of treatments by implantation have been performed on bones and tooth roots to afford good results in the remedy of the defects or recovery of functions thereof. However, there has not yet been obtained an articial bone or tooth root which satisfies the necessary requirements as material for living bodies, i.e. affinity to living bodies, safety, and excellent durability.
As metallic materials which have mainly been used for preparation of artificial bones or tooth roots, cobalt-chromium alloys, stainless steel, titanium and tantalum are exemplified. On the other hand, as ceramic materials, alumina or materials comprising predominantly carbon have been recently taken note of.
Although metallic materials have excellent mechanical strength, particularly impact strength, they are deficient in their affinity to tissues of living bodies. For example, when a metallic implant is used, metal ions are dissolved out therefrom in living bodies and affect a toxic action to bone cells around the implant. Furthermore, the bone-formation is obstructed probably because the thermal conductivity of the metallic implant is too high. Among the metallic materials, titanium and tantalum are particularly superior in a corrosion-resistance and hence have been employed as fixing plates for skulls or fractured parts of bones and implants for jawbones since about 1940, but these are not necessarily satisfactory.
To the contrary, ceramic materials show generally a good affinity to bones, and hence tissues penetrate into fine pores of the ceramic materials to afford a strong fixation, without reaction between the ceramic material and the tissue. Besides, they are also excellent in durability, that is, they are resistant to corrosion decomposition. On the other hand, they posses poor impact strength.
There has been proposed an implant having the characteristics of both of metallic materials and ceramic materials, i.e. an implant prepared by thermally spraying a ceramic material onto the surface of a metallic core material (cf. Japanese Patent First Publication Nos. 14095/1977, 82893/1977, 28997/1978 and 75209/1978). In these methods, however, a self-bonding type bonding agent is used in order to improve the adhesion of the ceramic coating layer. The bonding agent has a problem in that it contains nickel, chromium, etc. which dissolve out in living bodies and exhibit toxicity to living bodies.